1. Field of the Invention
The present invention relates to a scanning type microscope, and more particularly, to a scanning type microscope which is capable of recognizing a phase object.
2. Related Background Art
Various types of scanning type microscopes have been made commercially available because of their advantages, including the ease with which an electric signal is processed to obtain a plane image at a high resolution and the relatively simple structure of their optical system resulting from the correction of axial aberration.
Despite such advantages, the conventional scanning type microscope is not suitable for observing an object having a colorless, transparent phase structure. This limitation will be explained in detail in connection with FIGS. 1A and 1B, which exemplify a conventional; scanning type microscope.
In FIG. 1A, which illustrates the basic structure of a conventional scanning type microscope, a bundle of rays emitted from a laser 1 is condensed by a condenser 2 on an object 3, and the light coming from the object 3 passes through an objective 4 which guides the light to a photodetector 5 where its intensity is detected. The object 3 and the position on the object 3 at which the bundle of rays is condensed by the condenser 2 are moved relative to each other by a scanner 6. When the object 3 has a pattern with different transmittances, this scanning causes changes in the intensity of light received by the photodetector 5. The optical informtion obtained by the photodetector 5 is stored in the order of input in a signal processor 10, and the data stored is displayed on an indicator 11 such as a CRT as a plane object pattern image utilizing contrast or color tone difference.
In a case where a fine phase pattern having a slight phase difference exists on the object 3, there is no substantial difference in the intensity of light detected, and such a phase pattern therefore cannot be detected. FIG. 1B is a vector diagram for the light received by the photodetector, expressed on a complex plane using the amplitude and the phase. As shown in FIG. 1B the fine phase pattern retards the phase of light A1 by a very small angle .theta., relative to the phase of light A2. This is a very small phase shift, and there is substantially no difference in the intensity between the lights A1 and A2. As a result, the phase shift information generated by the phase pattern and corresponding to vector a cannot be detected.